Aperiodic coupling device



y 9, 1939- K. WILHELM 2,157,582

APERIODIC COUPLING DEVICE Filed March 20, 1957 INVENTOR K WI LH ELMATTORNEY Patented May 9, 1939 UNITED STATES PATENT GFFHQE APERIODICCOUPLING DEVICE m. b. H., Berlin, Germany Germany, a corporation ofApplication March 20, 1937, Serial No. 132,027 In Germany March 9, 19364 Claims.

It is known in the prior art to connect between antenna and a shieldedlead, for instance, for joint reception, an aperiodic amplifier. It iscommon practice to interpose between the said amplifier and thetransmission cable a transformer in order to step up the low resistanceof the cable. However, with amplifiers of this kind it is possible totransmit only a limited wave band range without a change of connectionsof the transformer.

According to this invention a tube of high mutual conductance, withwhose input electrodes the antenna is connected, works directly upon thefeeder cable which at its other end terminates in an ohmic resistance,the latter being equal to the characteristic impedance of the cable, ornearly so.

By the use of such a simple amplifier it is readily feasible to amplifya wave band from 15-30,000 meters without any change of connections sothat several receivers operating on widely different wavelengths can besupplied from the common aerial with signal potential. These receiversare suitably uncoupled from each other by the use of high-ohm voltagedividers or by tube stages, and these also may be built in a way as heredisclosed.

If the transmission cable has a characteristic or surge impedance of 150ohms, then the receiver end of the cable terminates in a resistance of150 ohms, with the result that the terminal resistance appears at theinput end as if no cable existed. When the dimensions are chosen as justindicated, standing waves and the incidental fluctuations or fading inreception at certain points of the wave band will be avoided.

According to the drawing, the plate circuit of the tube It in additionto the surge or characteristic impedance of the line and represented byZ, contains a resistance A which serves for the supply of the platepotential and which has a value that is a multiple of impedance Z, say,ten times higher, with the result that it plays no part in comparisonwith impedance Z.

If the mutual conductance value of the tube is 10 milliamperes per volt,and tubes of this kind are known in recent manufacture, then, for a linecharacteristic impedance of 150 ohms there is secured an amplificationof 10.150:1000=l.5. Actually, however, the gain insured with theamplifier is higher seeing that the full antenna voltage operates at thegrid, whereas, in case of direct connection of the feeder cable ordownlead with the aerial, because of the high inner resistance of theantenna and the low resistance of the cable, the cable low.

The condenser C must be chosen very large inasmuch as the outerresistance is very low, with the result that anti-regeneration for thelow fre- 5 quencies is liable to happen.

In order that the external resistance and thus also the amplificationmay be made as high as feasible, a cable having a high characteristicimpedance is preferably used, that is to say, a lowcapacity cable. Asshown the amplifier tube It] is of the pentode type the outer grid Hbeing connected with its cathode l2. A condenser l3 has one sideconnected to the control grid l4 and its other side connected to theantenna I 5 for transferring the signal voltage picked up onto thecontrol grid.

The shielded transmission line comprises a central conductor 16 enclosedwithin a shield I! which is connected to the grounded side of con- 20denser C as by a lead l8. The lower end of resistor A is also shownconnected to ground through a condenser D. The amplified signal voltageis transferred from the plate circuit of the tube to the centralconductor I6 by means of a condenser [9 which has a low impedance to thecurrents of all frequencies to be received.

Having described my invention, what I claim and desire to secure byLetters Patent is:

1. In a radio frequency distribution system adapted for operation over awide frequency band and wherein a thermionic relay of relatively hightransconductance is provided to act as an aperiodic amplifier, a remoteresistive load, means comprising a coaxial cable for connecting saidrelay device to the load, the inner conductor of the coaxial cable beingconnected for alternating currents directly to said relay device, saidload having an impedance which substantially matches the characteristicimpedance of the cable, the characteristic impedance of the cable beingconsiderably greater than the impedance thereof which would be suitablefor minimum attenuation.

2. In a radio frequency distribution system adapted for operation over awide frequency band and wherein a thermionic relay of relatively hightransconductance is provided to act as an aperiodic amplifier, a remoteresistive load, means comprising a coaxial cable for connecting saidrelay device to the load, the inner conductor of the coaxial cable beingconnected for alternating currents directly to said relay device, saidload having an impedance which substantially matches the characteristicimpedance of the cable, the

potential would be very characteristic impedance of the cable being ofthe order of 150 ohms.

3. In a radio frequency distribution system adapted for operation over awide frequency band and wherein a thermionic relay of relatively hightransconductance is provided to act as an aperiodic amplifier, a remoteresistive load, means comprising a coaxial cable for connecting saidrelay device to the load, the inner conductor of the coaxial cable beingconnected for alternat ing currents directly to said relay device saidload having an impedance which substantially matches the characteristicimpedance of the cable, the characteristic impedance of the cable beingrelatively high as compared to the characteristic impedance which isoptimum for minimum attenuation whereby there is developed from saidrelay device across the load a relatively large frequency independentvoltage.

4. In a radio frequency distribution system adapted for operation over awide range of frequencies and wherein a thermionic relay device of hightransconductance is connected to a remote resistive load through acoaxial cable Whose inner conductor is directly connected foralternating current to the relay device and whose characteristicimpedance is substantially equal to the resistance of the load, themethod of developing from the source across the load a relatively largevoltage substantially independent of frequency which consists in makingthe characteristic impedance of the cable relatively high as compared tothe characteristic impedance which is optimum for minimum attenuation,and substantially matching the load to said characteristic impedance.

KARL WILHELM.

